using System;

namespace Algorithms.Strings
{
    /// <summary>
    ///     <para>
    ///         Hamming distance between two strings of equal length is the number of positions at which the corresponding symbols are different.
    ///         Time complexity is O(n) where n is the length of the string.
    ///     </para>
    ///     <para>
    ///         Wikipedia: https://en.wikipedia.org/wiki/Hamming_distance.
    ///     </para>
    /// </summary>
    public static class HammingDistance
    {
        /// <summary>
        ///     Calculates Hamming distance between two strings of equal length.
        /// </summary>
        /// <param name="s1">First string.</param>
        /// <param name="s2">Second string.</param>
        /// <returns>Levenshtein distance between source and target strings.</returns>
        public static int Calculate(string s1, string s2)
        {
            if(s1.Length != s2.Length)
            {
                throw new ArgumentException("Strings must be equal length.");
            }

            var distance = 0;
            for (var i = 0; i < s1.Length; i++)
            {
                distance += s1[i] != s2[i] ? 1 : 0;
            }

            return distance;
        }
    }
}
